1. Field of the Invention
The present invention relates to a process for preparing glycine. More particularly, the present invention relates to an improvement in the process for preparing glycine in a short time by one stage reaction of a carboxy-methyl quaternary ammonium chloride, formed by reaction of monochloroacetic acid (hereinafter abbreviated to "MCA") with a tertiary amine, with an aminomethanol derivative (glycolloamine, methylolamine or hydroxymethylamine), formed by reaction of ammonia with formaline, in an aqueous solution, an alcohol solution or a mixed solution of both.
2. Description of the Related Art
Glycine (monoaminoacetic acid) is an amino acid which is most popularly used as an additive to processed foods for improving the taste and flavor and prolonging the storage period, a starting material for the synthesis of agricultural chemicals, a starting material for the synthesis of medicines, a starting material for the synthesis of other amino acids and an agent for preventing decomposition of vitamin C.
Glycine has heretofore been synthesized mostly according to the Strecker process in which aminoacetonitrile is synthesized by the ammonosis of glycollonitrile and the aminoacetonitrile is further hydrolyzed, but the process using MCA as the starting material is a classic bench-scale process which is considered to be economically disadvantageous. The reasons are as follows.
1) Since iminodiacetic acid and nitrilotriacetic acid are formed as by-products in addition to glycine by the reaction, the yield is low.
2) A large quantity of ammonia should be used.
3) The reaction time is long and it takes several days to complete the reaction at room temperature.
These defects are point out in Organic Synthesis, volume 1, page 300.
Various processes have been proposed and investigations have been published for overcoming these defects (see, for example, U.S. Pat. No. 3,190,914 (Jan. 22, 1965) and Japanese Examined Patent Publication No. 58-22055).
It is taught in the above U.S. patent that glycine is obtained in a yield of 80 to 90% by reacting MCA in an aqueous solution with an aminomethanol derivative produced by reaction of aqueous ammonia with a formalin solution. However, when this process is worked on a commercial scale, the following defects are observed. In case of the equimolar reaction, a long time is required and the yield is as low as 70%, and in order to elevate the yield to 90%, ammonia should be used in an amount of at least 3 moles per mole of MCA. Under this condition, however, excessive ammonia is bonded with hydrochloric acid formed by the reaction to form ammonium chloride and the operation of separating glycine after the reaction is rendered difficult, and for complete separation of glycine, such operations as concentration and crystallization utilizing the difference of the solubility between glycine and ammonium chloride should be performed repeatedly. The loss of glycine by this repetition of these operations is large, resulting in reduction of the yield.
In the process disclosed in Japanese Examined Patent Publication No. 58-222055, large quantities of ammonium carbonate and ammonium chloride are used for preventing formation of by-products, but a diacetic acid is still formed during the reaction, and the amount of used aqueous ammonia is more than 10 times the amount formed of glycine and the productivity per unit volume of the reactor is considerably low.
Furthermore, there is known a process in which a hexamine (hexamethylenetramine) is used instead of ammonia. Also in this process, the conversion is as low as about 70 to about 80%, and the separation of glycine after the reaction is inhibited by the hexamine having a low solubility.